Nickel-iron-zinc alloy electroplating



United States- Patent NICKEL-IRON-ZINC ALLOY ELECTROPLATING Charles L; Faust and William H'. Safranek, Columbus, Ohio, assignors, by mesne assignments, to Rockwell Spring and Axle Company, Coraopolis, Pa., a corporation of Pennsylvania N Drawing. Application July 1 0, 1957 Serial No. 670,871

8 Claims. c1. 204-43 This invention relates to nickel electroplating, particularly to a method'and plating bath for obtaining a leveling, ductile, and bright nickel alloy electroplate. This application is a continuation-in-part of copending U. S; patent application Serial No. 368,903, filed July 20, 1953', now abanbonded.

Nickel electroplates are conventionally employed as corrosion-resistant coatings for steel and as base plates upon which more attractive and resistant chrominum electroplates are deposited. Commonly, a flash coat or an extremely thin coating of copper is applied to the steel article to improve the adherence of the nickel. A thicker nickel, plate is then applied, followed by the chromium deposit. In the past, in order to obtain a bright and smooth-finish (level) electroplate, whether the electroplate consists of aplate of nickel alone or of a plate" of nickel followed by a plate of chromium, it hasbeen necessary to grind and polish the steel base material or the nickel electroplate, or both, to a relatively level and brightsurface. This is so because scratches, depressions, and imperfections on the surface of the steel or nickel are transferred t'o'the surface of the finished products Otherrequirements of nickel electroplating are the attainment of plates that possess a substantially even thickness and that are ductile. of complex shapes, areas of the cathode nearestthe anode receive a thicker electroplate and areas away from the anode receive a thinner electroplate than the average".

thickness of the deposit. This is caused by the fact that the areas nearest the anode have a relatively high cur rent density while the areas farthest from the anode" have a relatively low current density. Although these conditions exist in all nickel plating operations, the variations are different in different baths. The intensityof the condition in a given bath is referred to in terms of the Throwing power is, therefore, an important consideration.

in any nickel plating process. Ordinarily, acid' nickel plating baths possess good throwing power, but' manyfl brighteners are known to reduce the throwing power of" the bath.

In electroplating articles Nickel platw, and metallic plates in general, have a tendency to be in a stressed condition, resulting in cracks and unsatisfactory noncontinuous coatings. An ideal nickel plate is ductile or unstressed as well as brightand level.

V There has been much research and activity directed toward providing a ductile, level, and bright nickel electroplate that would reduce or eliminate the necessity of mechanically securing a bright and level nickel electrodeposit on a steel base material. Although somesuccess has been obtained by adding organic brightening agents to acid nickel baths, the known practices have resulted inelectroplates which lack at least one of the essential properties of ductility, leveling, and brightness. For. example, many known plating baths result in bright and ductile plates but are unsatisfactory from the standpoint of leveling. Also, many brighteners adversely affect the plating conditions, particularly the throwing power.

The electroplating bath and process of the present invention have been found to be far superior to those, of prior art practices in securing a ductile, level, and bright nickel electroplate and in providing grood throwing power. The planeness or levelness of a metal, surface may be measured by an instrument called a profilometer. This instrument provides an average reading of surface deviations in terms of root mean square (R. M. S.) microinches. Plating with nickel using prior art, bright nickel plating methods on polished steel plates with. R. M. S.1pr0filometer readings of 20 microinches, results in nickel plates with R. M- S. .profilometer readings of about 19 microinches. A desired bright, ductile plate would have a reading of 9 or less R. M. S. microinches. Nickel and nickel alloy plates deposited in accordance with the present invention are ductile, have bright to 'brillant mirrorlike finishes, and provide leveling to 6 microinches R. M. S. or less when applied to basis metal having a surface roughness of up to 20 R. M. S. microinches.

It is, therefore, a primary object of the present invention to provide a method and plating bath for obtaining a superior bright, ductile, and level nickel or nickel alloy electroplate. v g

It is also an object of the present invention to provide a nickel electroplating bath and process that reduce the necessity of bufling and polishing steel articles before electroplating in order to obtain adequate leveling.

Other objects and advantageous features will be obvious from the following specifications.

In general, the present invention relates to a process of electroplating and an. acid nickel electroplating bath in conjunction therewith wherein the bath contains a combination of brightening and leveling ingredients within critical concentration limitations that give level, ductile, and bright nickel plates while retaining good throwing power. The materials added to the bath are disulfonated as a buffer compound and a wetting agent.

. current is passed through the baths from anode to cathode, while the bath is agitated and heated, to efiect the from 0.03 to 1.25 g./l.; and iron within the range of from 0.3 to 5.6 g./l. Optimum results are obtainedby confining the plating bath to within a range of from 34 to 120 g./l. of nickel, a disulfonated benzopyrone in an amount equivalent to from 1 to 10 g./l. of coumarin disulfonic acid, 0.03 to 0.20 grams perliter of zinc ions, and 0.5 to 3.0 g./l. of iron ions.

Nickel salts predominate in the plating'bath. The bath should contain the usual incidental ingredients necessary to improve the efficiency of the plating operation, such An electric most satisfactory results. Minor impurities may be present without materially affecting the resulting nickel plate. Nickel salts may beprovided in the bath to provide the required range of nickel. Any suitable soluble nickel salts that will not interfere with plating conditions may be used in the bath... Most suitable salts are nickel fluoborates, nickel chloride, nickelcsulfamate, and nickel sulfate. Any or fall of these salts may be used in the same bath, but preferably, for ease of control, better efficiency and results, the preferred baths are those containing a chloride salt, fiuoborate salt, or a mixture of chlorideand sulfate salts. The nickel chloride salt used is preferably hydrated nickel chloride (Nichol-I However, NiCl can likewise be used. The nickel fluoborate added to the bath is generally obtainable in the form of a concentratedvs'olution containing from 40 to 45 percent nickelfluoborate, Ni(BF The nickel sulfate used is generally NiSO .6H- O.

Nickel within the ranges indicated can be obtained by providin'gabath containing .75 to 1000 grams of nickel sulfate (NiSO .6H O) .andfrom 25 to 60 g./l. of nickel chloride. (NiCl L6H O), the preferred ranges being from 150 to. 480 gJ/ l. of the;nicke1 sulfate and from 30 to 60 g./l. of the nickel'chloride.

The iron and zinc are codeposited with the nickel, resultingin anickel-rich plate having better protective properties, brightness, ductility and leveling properties than commercially purenickel plates. The total of the zinc and iron in the plate itself may vary from as little as 0.01 percent up toabout 40 per'cent but. preferably the total of these alloying metals is kept below 20 percent. The metal brightenersmay be added tothe bath in the form of any ionizing salts, such asthe chlorides, sulfates, or fluoborates. Itis not necessary that the saltcorrespond with the .nickel salt addition, i. e., ironor zinc chloridemay be added to nickel sulfate baths.

The disulfonated benzopyrone compound used is selectedfrom the grouplc'onsisting of disulfonated 1,2-

benzopyrone (coumarin), 2,1-beniopyrone (isocoumarin) and 1,4-benzopyrone (chromone). The structural formulas of these compounds before sulfonation are as follows:

2,1-benz'opyrone l,4-benzopyrone lsocoumarin chromone 1,2-benzopyrone (coumarin) When these compounds are sulfonated, the acid radicals (SO H) take various positions on a ring, depending on the nature of the compound and the position of the direct: ing groups. In thecase of coumarin, the radicals will be at the 6 and 3 positions. 1 The sulfonation of isocoumarin likely occurs at the 6th and 7th or 7th and 8th positions.

When chromone is sulfonated, addition probably occurs i at the 6th position and one of the 2nd, 3rd, or 8th positions.

It is also possible to use salts of such acids, the substitution products thereof, and crude-mix sulfonation products, as well as the disulfonic acids themselves. These materials are to be included in the term disulfonated benzopyrone as used herein. Examples of suitable compounds are the sodium and nickel salts of coumarin disulfonic acid; sodium and nickel salts of chromone disulfonic acid; sulfonated derivatives of benzopyrones and substitution products thereof; as the acid or salt of 3- methyl coumarin; 4,8 dimethyl coumarin; 6 chlorocoumarin; 3 acetylcoumarin; and 7 hydroxy coumarin. It will also be apparent that other alkyl, halo, and hydroxy derivatives of disulfonated coumarin, chromone, isochromone, etc., can be employed. These sulfonated benzo pyrone compounds can be used singly or mixed together.

The disulfonated products of benzopyrone may be added to the baths of the present invention in any convenient form. For example, the addition may be made in the form of the sodium salt of coumarin disulfonic acid, the nickel salt of coumarin disulfonic acid, or it may be the reaction product of coumarin and fuming sulfuric acid.

The preferred addition is the nickel salt of coumarin disulfonic acid; In preparing such compound or reaction product, some nickel salt of coumarin monosulfonic acid will usually be present. This is because it is difficult to obtain a complete reaction in attaining the disulfonic product. It is not necessary, however, to separate the monoacid from the diacid, as the plating bath will tolerate a considerable portion of the monoacid without deleterious effects to the plating or resulting nickel alloy plate.

; Although the presence of the monoacid is notharmful in quantitiesequal to that of the diacid, an excess of monoacid is undesirable. It is, therefore, preferable-that the sulfonated portion of the coumarin sulfonic acid product contain about 50 percent or more of the diacid. The preferred range of the product may be defined as from 2 to 20 g./l.' of a coumarin sulfonic acid product, the sulfonated portion of which contains approximately 50 percent or more of the disulfonic acid.

Suitable sodium salts of coumarin sulfonic acid pr0ducts can be readily prepared in the following manner:

grams of coumarin are addedto 500 grams of fuming sulfuric acid (20 to 30 percent excess 50;) while stirring the mixture which is heated to between 96 and 98 C. After reacting for two hours, the hot mixture is cooled to 25 C. This product is capable of being used directly in the plating bath but neutralizing agents may be added to provide a proper pH. To make the sodium salt, the product is cooled to 5 C., and then slowly added to 800 milliliters of a saturated sodium chloride solution, cooled to between 0 and 5 C. After letting the mixture stand over night, the precipitate is removed by filtration, washed with saturated sodium chloride solution, purified. by recrystallizing twice in hot water, and allowed to dry over night in an oven at 100 C.

To prepare the nickel salts, the reaction product of coumarin and fuming sulfuric acid is reacted with nickel carbonate instead of sodium chloride.

The active metals and sulfonated benzopyrone product can be conveniently added to the bath together; for example, an easy way to make additions of zinc and coumar-in disulfonic acid at the same time is to add to the bath a solution prepared by reacting zinc oxide with the acid sulfonation product of coumarin. The ratio of zinc to coumarin sulfonic acid can be adjusted to any desired value. The ratio of 1 to 10 is convenient for formulating a new bath and for replenishing materials consumed while the bath is being operated. Much of the excess sulfuric acid is neutralized when zinc is added to the acid sulfonation product of coumarin when preparing a solution with one part of zinc and two parts of coumarin sulfonic acid. The remaining excess sulfuric acid can be certain of theseadditions eflect significantly better plating H conditions in the form of throwing power of bath. 7

Table l'shows the effects of additions of one or more of the additives, coumarin disulfonic .acid, zinc,and iron within the critical. ranges contemplated by the present invention to acid nickel baths.

It is, apparent fromTable 1 that theacid nickel baths without additions possess no detectable leveling power and the lating 1.

do not producebright 'e'lectroplates and thatthe addition of coumarin disulfonic acid alone has no detectable effect on leveling or brightness. However, the acid nickel baths. with or without the addition of coumarin disulfonic acid alone have higli'throwing power properties and resultiii ductile plates. The addition of 'Zn alone destroys throwing power and ductility but effects a slight improvement in leveling and brightness. The addition of iron alone reduces throwing power and ductility while offering no I improvements in leveling or brightness. The addition of both coumarin disulfonic acid and zinc improves leveling and brightness 'to some extent but reduces throwing power and ductility. The addition of both coumarin sulforiic acid and iron effects a broad range of brightness and does not adversely change theductility or throwingpower but does not provide a bath with adequate leveling, Tlref bath containing all three of the additions of the-present invention provides the best plating conditions available. A buffer is usually added to the acid nickel plating bath to prevent sudden changes in the pH whichcould adversely affect the results- Buffers customarily used in the art can be added to the bath I TABLE 1- Ingredients, grams per liter Throw- Cou- Leveling Bright range ing Ductility marin power I disul- Zn 'Fe 7 ionic acid 0 0 Excellent. '0 :Do/

2.5 0.2 Good. 2.5 0 Excellent.

None=no detectable brightnessrange or'leveling effect.

Fair=some leveling efi'ect but not significant; adequate throwing power but not so good as in baths without additions.

Excellent=significant1y improved leveling; best ductility, attainable.

Good=satisfactory throwing power or ductility but not the best ductility attainable.

Poor=unsatisfactory and commercially nonacceptable leveling, throwing power, or ductility. I

disclosed herein in amounts to properly effect the bu'fling actionl It has been found best to employ boric acid. Fro-n1 apractical standpoint, the amount of buifer generally may be from 10 to 60 g./l., although best results in control, economy, and plate conditions areobtained with'concentrations of from to g./l.

A wetting agent is desirable to prevent pitting of the plates and is generally used in the baths of this invention.

Agents previously known to prevent pitting in nickel plates are satisfactory. It will be understood, however,

that such agents must not adversely affect the baths, oper-- ating conditions and resulting electroplates. An example of a suitable wetting agent is sodium lauryl sulfate. Only a minor amount need be added to the bath to prevent pitting, and large amounts are unnecessary and wasteful. Generally, from 0.1 to 1.0 g./l.of wetting agent can be present in the bath, although from 0.2 to 0.5 g./l. is best for preventing pitting of the surfaces.

The pH of the bath is adjusted by adding to the bath a suitable acid, such as hydrochloric or sulfuric acid, or a suitable alkali, such as nickel carbonate, nickel hydroxide,

or zinc oxide.

The pH of the bath should always be on the acid side and preferably should not exceed about 5 for any appreciable period of time. It should never be below about 1.9 or the bath would be thrown out of balance, and the composition, levelness, and brightness of the plate would be adversely altered on continued operation. It has been found that the'best bath stability and resulting platefcohditions are accomplished by maintain v ing the pH of the bath at from 2.5 to 4.5.

The bath shouldalways be agitated during plating in order to consistently obtain leveling plates having a bright "mirrorlike appearance.

Soluble metal anodes, such as anodes of nickel, may be used. Alloy anodes may include nickel alloys con taining iron and zinc which substantially replenish the ,bath. Current densities for the anodes should be sulficient to provide the correct dissolution, and, for must purposes, can rangefrom 5 to amperes per square foot. 'It is preferred to maintain the anode current density in the range of from 20 to 40 amperes per square foot in order to obtain the best results from a commercial stand- --point. H Operating cathode current densities from 20 to 100 or more amperes per square foot can be used in the present method although from a practical and commercial standpoint it has been found best to employ current densities in the rangeof from 30 to 60 amperes per square foot.

The plating should be carried on for at least about 5 minutes. For better leveling effect, at least 15 minutes 7 operation is required. The plating can continue for as preferred temperature range is from 125 to 145 F.

The following specific examples illustrate the plating baths of the presentinvention, but do not restrict the present invention to the exact compositions and conditions set forth.

Table 2 shows five nickel plating baths containing sul- .fonated coumarin product, iron, and zinc as the brightening and leveling agents. The sulfonated coumarin was produced by sulfonating one part coumarin with five parts of 20 percent oleurn (a solution of H and about 20 percent, by weight S0 The resulting reaction product that was used as the recited addition had a coumarin disulfonic acid content of approximately 15 percent. The coumarin monosulfonic acid contentof the reactive product was also about 15 percent. The wetting agent solution fXXXD was a solution of sodium lauryl sulfate made by The I-larshaw Chemical Company. All of the baths produced ductile mirror-bright nickel plates on pol ished steel sections. a V

Table 3 sets forth four examples of nickel plating baths containing nickel coumarin disulfonate, iron, and zinc as the brightening and leveling agents. .T he sulfonated portion of the sulfonated coumarin reaction product employed contained about 50 percent of the disulfonated acid and about 50 percent of the monosulfonated acid. All of the baths produced bright ductile plates on polished steel.

The following is an eirample of a plating bath with chlorocoumarin nickel sulfonate (believed to contain TABLE Bath constituent Nlckelsuli'ate, ieisoi-cmo, gL/i--- Nickel chloride, NiCls-(iHgO, g./1- Borlc acid, HsBOI, i;

Sulionated ooumarin pioducggjlt i 7.

Ferrous sulfate, FeSO4-7Hl0.... Equivalent iron concentration, g./l Zinc sulfate, ZnSO4-7H O, g./l.-..". 1.1. Equivalent zinc concentration, gJl. Wetting agent solution (XXXD),

percent y volume. 1 1 pH 3.1 to 3.9 3 i to 3.0 2.1 to 2.7 Operating condition: 1

Temperature, F. 130 to 133 130 to 1' 130 to Oathod/e fiurrent density, tom 30 to to amp. sq. Agitation (horizontal paddles -0. P. M., 4%- 60-0. P. M., 4%-inch 60-0. P. M., 4%-inch 600. P. M., 4% 60-0. P. M., 4%

, moving up and down). inch stroke. stroke. stroke. inch stroke. inch stroke.

Plating time, minutes. 60 00 45 30. Thickness 01 plate, inch 0.0015- 0.0015 0.0015 0.0015 0.0015. Surface roughness (profilometcr) measurements:

Begin-14: plating, R.M. S. micro- 11 to 1 8 to 17 13 to 11 to 10 14 to 19.

0 es. Aigfrhplating, R. M. S. micro- 1% to 3 to 5 2 to l 3 to 4 4 to 5.

0 es. Plate composition Not determined.. 83% Ni, 14% Fe, 3% Zn... 82% Ni,14.4% Fe, 3.7% Zn. Not determined.. Not determined.

TABLE 3 Bath constituent VI VII VIII IX Nickel sulfate, NlSOi-fiHiO, g./l.--. 360 300 360 360. Nickel chloride, Ni0l-6H;O, gull... 7 7 75. Boric acid, 11,130 g./l- 42 4 42 42. Nickel ooumarin sulionate, the sul- 0 6 6 7.1.

lonatedxortion of which contain ed 50% isulionate and 50% monosultonate, g./i. Ferroussuli'ate, FeSO4-7Hz0, g./l..- 10.0-.. 10.0-. 9.5... 4.5. Equivalent iron concentration, g./l. 2.0..- 2.0-.-. 1.9.. 0.9. Zinc sulfate, ZnSO4-7H1O, g./l 0.6.-- 0.5-. 0.75-.. 0.7. Equivalent 11110 concentration, g./l. 0.13... 0.11.. .17.- 0.15. Wetting agent solution Altm1t41%, by volume 3.1 Aitmt21%, by volume 3.0 About 1%, by volume 3.3. About 1%, by volume 3.2.

o o Operating condition:

Temperature, "F 135 to 140 .4. to 137 135 to 140. Cathcaie current density, amp./ 50 to 00 60 to 7 40 to 42 50 to 60.

sq. i Agitation-.. Work bar: 35 0. I. M., 6- Mechanical stirring Tumbled in Lucite barrel Work bar: 45 0. P. M., 4-

, inch stroke. rotating at 5 C P M inch stroke. Plating time, minutes 20 5. Thickness of plate, inch 0.001--. 0.0002. Basis metal Polished steel Coppggplated zinc die coa gs. Appearance of plate Mirrorlike-no polishing Mirrorlike, smooth. Bright and smooth Mirrorlike, smooth.

scratches evident. Approximate composition of pla e 90% Ni, 9% Fe, 1% 211.... 90% Ni, 9% Fe, 1% Zn.. Not determined Not determined.

Operatingconditions: V

- Cathode current density 50 amp/sq. ft.

. Temperature.. to F.

Agitatiom'" Mechanical stirrer.

Plating time 25 minutes.

Bright plate and leveling of surface irregularities were obtained with the above conditions. Plate composition was not determined.

about 50 percent nickel monochloro, disulfono coumarin):

Example XI Nickel sulfate, NiS O .6HgO g./l 300 Nickel chloride, 'NiCl .6H O g./l 30 Boric acid, H BO ..g./l 41 Ferrous sulfate, FeSO .7H O g./l 10.0 Equivalent iron concentration g./l 2.0 Zinc sulfate, ZnSO I 7I-I O; g./l 0.5 Equivalent zinc concentration g./l 0.11

I Wetting agent solution (XXXD) percent by volume..- 1.0 pH 2.9 to 3.5 Nickel chlorocoumai'in sulfonate ..g./l 6

Usinga work-bar agitating at 53 C. P. M. with a 3 /4-inch stroke, leveling was measured at different current densities and temperatures, with the results shown in Table 4. All plates were mirrorlike and ductile. Plate composition was not determined.

Example XII Exceptionally good plates were obtained with iron and zinc using a plating bath prepared as follows:

BLE. 4

EFFECT OF OHLOROCOUMARIN NICKEL SULI ONATE ON LEVELING AT VARIOUS OPERATING CONDITIONS Current Zine in bath, g./1. Temp, density, Leveling,

g/F. amp./ percent sq. ft.

N Mar-Thickness of all plates equal to 0.001 inch.

percent leveling 100(B A) B M. S. profilometer reading in microinches before plating With a temperature of 136 F., a pH of 3.8, an anode current density of 20 amp/sq. ft., a cathode current density of 30 amp./sq. ft. and with the solution agitated with Bakelite paddles reciprocating about 54 C. P. M. with a 4-inch stroke, a uniformly mirrorlike plate, 0.00095- inch thick measuring 2.5 R. M. S. microinches was obtained on a steel bumper-bar segment measuring 11 R. M. S. microinches before plating. The plate contained approximately 3 percent iron and 3 percent zinc.

A plating bath using sulfonated 1,4-benzopyrone or chromone was formulated as follows:

7 Example XIII Components: Amount Nickel sulfate (NiSO .6I-I O) g./l 360 Nickel chloride (NiCl .6H O) g./l 30 Boric acid (H BO g./l 42 Iron sulfate (FeSO .7H O) g./1 5.5 Equivalent iron concentration g./l 1.1 Zinc sulfate (ZnSO g./l 1.25 Equivalent zinc concentration g./l 0.5 Product of sulfonating 1 part chromone with 5 parts fuming sulfuric acid g./l l8 XXXD percent by volume 1 Water Balance The pH of the bath was adjusted to 2.9 and the tern perature thereof was maintained at about 130F. With the anode at a current density of 10 amp./ sq. ft. andthe cathode at a current density of 20v amp./ sq. ft. and being moved with a 39inch stroke at 60 CJP. M., a nearly mirror-bright, very ductile nickel plate 0.00l5-inch measuring 6 R. M. S. microinches over steel measuring 9 R. M. S. microinches was produced.

The invention is not limited to the preferred embodiment but may be otherwise embodied or practiced within the scope of the following claims.

We claim:

1. A bath for depositing a nickel alloy electroplate, comprising an acidic aqueous solution of about 17 to 233 g./l. of nickel ions, about 0.3 to 5.6 g./l. of iron ions, about 0.03 to 1.25 g./l. of zinc ions, and a disulfonated benzopyrone in an amount equivalent to about 1 to 10 g./l. of coumarin disulfonic acid.

2. A bath' for depositing a nickel alloy electroplate, comprising an acidic aqueous solution of about 34 to 120 g./l. of nickel ions, about 0.5 to 3.0 g./l. of iron ions, about 0.03 to 0.20 g./l. of Zinc ions, and a disulfonated benzopyrone in an amount equivalent to about 1 to 10 g./l. of coumarin disulfonic acid.

3. A bath for depositing a nickel alloy electroplate, comprising an acidic aqueous solution of. about 17 to 233 g./l. of nickel ions, about 0.3 to 5.6 g./l. of iron ions, about 0.03 to 1.25 g./l. of zinc ions, and a sulfonated benzopyrone product, the sulfonated portion of which contains at least about percent by weight of disulfonated benzopyrone, said sulfonated benzopyrone product being present in an amount equivalent to about 1 to 10 g./l of coumarin disulfonic acid.

4. A bath for depositing a nickel alloy electroplate, comprising an acidic aqueous solution of about 34 to 120 g./l. of nickel ions, about 0.5 to 3.0 g./l. of iron ions, about 0.03 to 0.20 g./l. of Zinc ions, and a sulfonated benzopyrone product, the sulfonated portion of which contains at least about 50 percent by weight of disulfonated benzopyrone, said sulfonated benzopyrone productv being present in an amount equivalent to about 1 to 10 g./l. of coumarin disulfonic acid.

5. In a process of depositing a nickel alloy electroplate, I

233 g./l. of nickel ions, about 0.3 to 5.6 g./l. of iron ions,

about 0.03 to 1.25 g./l. of zinc ions, and a disulfonated benzopyrone in an amount equivalent to about 1 to 10 gI/l. of coumarin disulfonic acid.

6. In a process of depositing a nickel alloy electroplate,

the step of passing an electric current through an electrolyte between an anode and a cathode, said electrolyte comprising an acidic aqueous solution of about 34 to g./l. of-nickel ions, about 0.5 to 3.0 g./l. of iron ions,

about 0.03 to 0.20 g./l. of zinc ions, and a disulfonated benzopyrone in an amount equivalent to about 1 to 10 g./l. of coumarin disulfonic acid.

7. In a process of depositing a nickel'alloy electroplate,

contains at least about 50 percent by weight of I disul fonated benzopyrone, said sulfonated benzopyrone product being present in an amount equivalent to about 1 to 10 g./l. of coumarin disulfonic acid.

8. Ina process of depositing a nickel alloy electroplate,

the step of passing an electric current through an electrolyte between an anode and a cathode, said electrolyte comprising an acidic aqueous solution of about 34'to 120 g./l. of nickel ions, about (1.5 to 3.0 g./1. of iron ioils, al ut;0.03 to10.20 g./1. of zinc ions, and a sulfonatcd benzopyrone product,flthe sulfonatlcd portion of which contaiusflatleastabout -50 percient by weight of disulfonatedbcnmpyrone, said sulfonated benzopyrone prod- 5 net being prcsentin an amount equivalent to about 1 to 10 g./l. of coumarin disulfonic acid.

References Ci t edin the file of this patent UNITED STATES PATENTS Burns et a1 Dec. 22, 1931 Rlissell May 22, 1934 Donroe Apr. 15, 1947 Brown July 4, 1950 Brown Nov. 9, 1954 Safranek Oct. 8, 1957 

1. A BATH FOR DEPOSITING A NICKEL ALLOY ELECTROPLATE, COMPRISING AN ACIDIC AQUEOUS SOLUTION OF ABOUT 17 TO 233 G./L. OF NICKEL IONS, ABOUT 0.3 TO 5.6 G./L. OF IRON IONS, ABOUT 0.03 TO 1.25 G./L. OF ZINC IONS, AND A DISULFONATED BENZOPYRONE IN AN AMOUNT EQUIVALENT TO ABOUT 1 TO 10 G./L. OF COUMARIN DISULFONIC ACID. 